1. Field of the Invention
This invention relates to a method for stabilizing organic substrates against light, and more specifically, to a method for stabilizing organic compounds, especially organic dyes, against light.
2. State of the Art
It is generally known that organic substrates, for example organic dyes, tend to fade in color or discolor when subjected to the action of light. Investigations have been made in the fields of inks, textile dyeing, color photography, etc. to prevent color fading or discoloration of organic dyes, namely to increase their light fastness. The present invention is used very advantageously to increase the light fastness of the organic substrates.
In the present specification and the appended claims, the term "organic substrate" or "substrate compounds" include substances which look colored or colorless to the human eye under sunlight. They include substances having an absorption maximum in the visible region, such as fluorescent whitening agents, and substances having an absorption maximum in the infrared region. In the present invention, the organic substrates include organic substances having an absorption maximum at about 300 nm in the ultraviolet region to about 800 nm in the infrared region.
In the present specification and the appended claims, the terms "color" or "dye" include organic substances which appear colored to the human eye under sunlight. In the present specification and the appended claims, the term "light" denotes electromagnetic radiation having a wavelength of less than about 800 nm and includes ultraviolet rays having a wavelength of less than about 400 nm, visible rays having a wavelength of about 400 nm to about 700 nm, and infrared rays having a wavelength of about 700 to about 800 nm.
The present invention is particularly directed to improving the light fastness of organic substrate materials occurring in photographic materials, e.g., color films, prints, etc., in colored polymers useful as agricultural vinyl cover sheets, umbrellas, tents, etc.; of fluorescent whitening agents; and dyed textiles, etc.
It has been known that organic substrates, such as colors or dyes, tend to fade in color or discolor under light. Many reports have disclosed methods of reducing color fading or discoloration, and increasing light fastness. For example, U.S. Pat. No. 3,432,300 discloses that the light fastness of organic compounds such as indophenol, indoaniline, azo and azomethine dyes to visible and ultraviolet light can be improved by mixing them with phenolic compounds having a fused heterocyclic system.
Generally, in the field of silver halide photographic materials, azomethine dyes or indoaniline dyes are formed by the reaction of the oxidation product of an aromatic primary amine developing agent with a coupler, as described in Chapter 17 of C. E. K. Mees and T. H. James, "The Theory of the Photographic Process" (published in 1967 by Macmillan). A number of methods are known for improving the stability to light of images formed from these dyes, i.e. color images. For example, it is known to use hydroquinone derivatives described, for example, in U.S. Pat. Nos. 2,360,290, 2,418,613, 2,675,314, 2,701,197, 2,704,713, 2,728,659, 2,732,300, 2,735,765, 2,710,801 and 2,816,028 and British Pat. No. 1,363,921, gallic acid derivatives described, for example, in U.S. Pat. Nos. 3,457,079 and 3,069,262 and Japanese Patent Publication No. 13496/68; p-alkoxyphenols described, for example, in U.S. Pat. Nos. 2,735,765 and 3,698,909; and coumarone or coumarane derivatives described, for example, in U.S. Pat Nos. 3,432,300, 3,573,050, 3,574,627, 3,764,337, 3,574,626, 3,698,909 and 4,015,990. These compounds have an effect of inhibiting the color fading or discoloration of color images, but the effect is still insufficient.
A method for improving the stability of an organic substrate compound to light by using an azomethine quenching compound having an absorption maximum more bathochromic than the absorption maximum of the substrate compound is disclosed in British Pat. No. 1,451,000. The method, however, is disadvantageous because the azomethine quenching compound itself is strongly colored, and greatly affects the color of the substrate compound.
The use of a metal complex for prevention of the photodegradation of polymer is described by J. P. Guillory and R. S. Becker in J. Polym. Sci., Polym. Chem. Ed., 12, 993 (1974), and by R. P. R. Ranaweera and G. Scott in J. Polym. Sci., Polym. Lett. Ed., 13, 71 (1975). Furthermore, a method for stabilizing dyes by metal complexes is described in Japanese Patent Publication No. 87649/75 and Research Disclosure 15162 (1976). However, these complexes do not have very great discoloration preventing effects and their solubility in organic solvents is low. It is therefore impossible to add them in amounts high enough to produce a sufficient fade inhibiting effect. These complexes also suffer the defect that because they are strongly colored, they will cause deleterious effects on the color purity of the organic substrate substances, especially dyes, when they are added in large amounts.